« PreviousContinue »
increase in the total flora of the pot with grass-roots added (as shown in column 7). They are therefore omitted from the table.
TABLE II. - ACTINOMYCETES IN DUNKIRK SILTY CLAY LOAM, WITH and WITHOUT
ADDITION OF GRASS-ROOTS.
TOTAL COLONIES PER
TIME SINCE ADDITION OF GRASS-ROOTS
FIRST ADDITION 1 day.
No. 1) 3,000,000 2,200,000 800,000 6 days.
No. 1 *1,700,000 ?2,100,000 ? 14 days.
No. 1 6,000,000 3,500,000 2,500,000 23 days.
No. 1/ 4,000,000 2,500,000 1,500,000 3 mo., 7 days. No. 1 6,000,000 1,700,000 4,300,000 3 mo., 20 days.. No. 11 6,000,000 3,200,000 2,800,000 3 mo., 20 days. No. 216,000,000 3,000,000 3,000,000 4 mo., 7 days. No. 1 5,300,000 2,000,000 3,300,000 4 mo., 15 days.... | No. 1 6,300,000 3,500,000 2,800,000 4 mo., 15 days.. No. 21 4,500,000 3,100,000 1,400,000 7 mo., 15 days.. No. 1 6,200,000 2,900,000 3,300,000 7 mo., 15 days.. No. 21 8,000,000 4,000,000 4,000,000 10 months.
No. 11 5,000,000 2,500,000 2,500,000 10 mo., 7 days.. No. 24,300,000 2,700,000 1,600,000
30,000,000 22,000,000 1.7:1 80,000,000 30,000,000 1.6:1] 35,000,000 20,000,000 3.5:1 43,000,000 13,500,000 1.9:1 31,000,000 32,500,000 2 :1 29,000,000 23,000,000 2.6:1 33,000,000 19,000,000 1.8:1 23,500,000 24,000,000 1.5:1 22,000,000 18,000,000 2.1:1 30,000,000 16,000,000 2 :1 32,500,000 28,000,000 2 :1 14,000,000 8,000,000 1.6:1 20,000,000 9,500,000
4 days. 23 days.. 3 mo., 20 days.. 5 months. 6 months
No. 2 *2,300,000]?1,800,000 500,000 *1.3:1? 75,000,000 7,000,000
* These counts are inexact because on this date the plates made from the pot with grass-roots liquefied too rapidly to permit a satisfactory count.
† The figures obtained during the first week after the addition of grass-roots are omitted from this average.
# The second lot of grass-roots was added to the previously treated pot of set No. 2 ten and half months after adding the first lot.
As shown in this table, the Actinomyces-content of the untreated pots remained almost constant thruout the experiment, averaging 2,900,000 colonies per gram during the first ten months. The Actinomyces-content of the pot with grass-roots, however, increased to 6,000,000 in two weeks and remained at about that height during the ten months (average 5,500,000 per gram). The average difference in Actinomyces-content between the two soils after the first two weeks was 2,750,000. The average ratio of the Actinomyces-content of the soil with grass-roots to that of the untreated soil was 2.03:1. Similarly, in Technical Bulletin No. 52 (Table II), in 34 comparisons of sod and cultivated spots of various soil types, the average ratio is 2.15:1. This similarity suggests that dead grass-roots mixed with soil cause the same stimulation to the Actinomycetes as brought about by grass growing on the soil.
It must be noticed, however, that the Actinomycetes are not the only organisms stimulated by the presence of the grass-roots. Fourteen days after the addition of the roots the total count was 80,000,000, while in the check pot it was only 30,000,000. Nearly all of this increase (altho this fact is not brought out by the data given in Table II) was due to an increase in the number of nonspore-forming bacteria in the soil with grass-roots, the number of spore-formers remaining practically constant thruout the experiment. The number of non-spore-forming bacteria remained higher in the soil with grass roots than in the untreated soil until about four and a half months after the treatment. This indicates that non-spore-formers, as well as Actinomycetes, take part in the decomposition of grass-roots, a fact still further brought out by the data in lower section of the table.
In the lower section of the table are given some further figures obtained by plating the soil in the pots of set No. 2 in the above experiment. Ten and a half months after beginning the experiment, one of these two pots containing grass-roots was further treated by adding a second, and larger, lot of grass-roots. On the same date the soil in the other pot of this set was also aerated and then returned to the pot without further treatment so as to serve as a check. It was found that the aeration alone did not affect the Actinomyces-content or the total count of the check pot; but that 23 days after treatment, the soil with grass-roots showed a count of 12,500,000 Actinomycetes per gram, six times that of the check pot. The total count had meanwhile increased to the unusually high figure of 130,000,000 per gram. As the spore-forming bacteria remained constant in numbers, it is evident that the high total count must have been due largely to a great increase in non-spore-forming bacteria. In other words, both Actinomycetes and non-sporeformers increased in number after the addition of grass-roots, and presumably both groups took part in their decomposition. Later the non-spore-forming bacteria decreased somewhat altho by no means to their original numbers, while the Actinomycetes remained fairly constant in number and about five times as abundant as in the check pot.
Two explanations of these results are possible. On the one hand it may be assumed that the non-spore-formers are more active in the early stages of the decomposition of grass-roots, the Actinomycetes in the later stages; or on the other hand the explanation may be that both groups multiply at first, and then later decrease in activity, but that no decrease in Actinomyces colonies is observed because of the comparative longevity of their conidia.
Some information on this point has been obtained from another experiment. Sod soil, showing a high plate count of Actinomycetes, was air-dried, and sifted thru a fine sieve so as to remove all but the smallest fragments of roots, then placed in a pot, brought up
to its original moisture content and later watered at intervals. When it was last sampled, fourteen months after beginning the experiment, the Actinomycetes were still as high in numbers as in a check pot (from which the grass-roots had not been removed) and still comprised 40 per ct. of the total flora developing on the plates. This indicates that a soil may continue to show a high plate count of Actinomycetes for some time after the condition which stimulated their numbers has ceased to affect them. It suggests that their high numbers in sod soil may be due in part to the fact that their conidia are comparatively long-lived.
In brief, the experiments carried on to investigate the relation of Actinomycetes to grass-roots are inconclusive. They merely indicate that these organisms, like the non-spore-forming bacteria, take active part in some of the processes going on in normal soil, and are not inactive under such conditions, like the spore-forming bacteria.
GENERAL DISCUSSION OF THE WHOLE SERIES OF SOIL
FLORA STUDIES. The chief fact emphasized by these soil flora studies is the meagerness of present-day knowledge in regard to the micro-organisms of soil. The bacteria that have been shown to carry on nitrogen transformations and other activities known to occur in the soil and have therefore been given the most thoro study, do not seem to be especially numerous in soil, and it has never been shown that their numbers in soil increase while the activities ascribed to them are taking place. On the other hand, the bacteria that are numerous in soil and do multiply at times when great bacterial activity should be expected are organisms concerning which almost nothing is yet known.
One of the first steps necessary in order to put the knowledge of soil bacteria on a scientific basis is classification. It is difficult to make definite? described species. Statements frequently found in the literature in regard to the activities of certain soil micro-organisms are almost valueless to anyone except their author, because of the uncertainty as to the identity of the organisms studied. This confusion can be prevented in the future only by the development of a classification of the soil micro-organisms based upon the accumulation of thoro characterizations of the common species.
The species of soil bacteria that have been most thoroly characterized in the past are certain spore-forming bacteria. The sporeformers, however, are not so abundant or apparently so important as the other groups of organisms developing on the plates. Among these other groups — the non-spore-forming bacteria and the Actinomycetes - very few species have ever been thoroly characterized.
The difficulties to surmount in characterizing species among these organisms are great. Morphology has proved a great help in classifying the spore-formers; but morphological characters are of little help in the classification of the non-spore-formers, and they have not yet been successfully used in classifying the Actinomycetes. Physiological tests have been the basis of classification of certain kinds of bacteria (the B. coli group, for instance); but the ordinary physiological tests used to characterize bacterial species are not applicable to the majority of soil bacteria.
For this reason but few of the types described in this series of bulletins can be considered as species. Further classification must be undertaken, and the efforts of no one man will be enough to put the matter on a sound basis. It must be remembered, moreover, that systematic studies of soil bacteria are no more important than physiological studies. Neither is of much value without the other, and the results of one should be used to interpret the results of the other.
Physiological and systematic studies both depend upon cultural methods and upon the assumption that the organisms investigated are the active organisms in soil. There is need of some direct method of investigating the soil micro-organisms that can be used to check up the cultural methods. Within the last few months the writer has called attention to a method of using the microscope for the direct examination of bacteria in soil.33 The weakness of this microscopic method lies in the fact that it is not possible to isolate the organisms thus revealed and there is no way of studying their activities. Nevertheless the method promises good results if used in conjunction with plate culture, and in continuing these flora investigations microscopic findings are to be compared with those obtained by cultural methods.
33 Conn, H. J. The direct microscopic examination of bacteria in soil. Abstr. of Bact., 1: No. 1. 1917.
For many years the Official Dairy Instructors Association, which has recently become the American Dairy Science Association, has maintained a committee on dairy score card, which committee is responsible for the so-called " official" dairy score card. In 1912 this committee recognized the necessity for a different score card evaluating the quality of milk rather than the conditions under which milk was produced, and formed a subcommittee to study this problem. This subcommittee was later made an Association committee on milk quality. Extensive investigations have been conducted, particularly at the New York Agricultural Experiment Station and the Illinois Agricultural Experiment Station, at Urbana, in connection with this study, and the present publication is an analysis of the problem of milk quality as it appears to this committee after these years of study.
H. A. HARDING,
College of Agriculture and Agricultural
R. S. BREED;
New York Agricultural Experiment
W. A. STOCKING, JR.,
New York State College of Agriculture and
E. G. HASTINGS,
College of Agriculture and Agricultural