282 



SCIENCE 



[N. S. Vol. XLIV. No. 1130 



is reduced throughout most of its extent to an 

 ependymal layer. Small localized thickenings 

 may occur but nothing corresponding to the 

 normal animal. 



The difference in size and structure between 

 the thyroid of an albino and that of a check 

 is very marked. The thyroid of a normal 38 

 mm. tadpole with 4.0 mm. hind legs is approxi- 

 mately three times the size of a 37 mm. albino 

 with 0.1 mm. hind legs. The compactness and 

 character of the parenchyma show an even 

 more striking contrast. A sagittal section 

 through the thyroid of a 38 mm. check shows 

 on an average 15-18 vesicles, many of which 

 are largely distended with colloid, the par- 

 enchyma of the whole gland being compacted 

 together, as compared with that through the 

 thyroid of a hypophysectomized 37 mm. speci- 

 men which shows 4-5 atrophied vesicles con- 

 taining but a slight amount, or no colloid, and 

 with large spaces between the vesicles. The 

 cells making up the vesicles of the former are 

 cuboidal and protoplasmic-rich, in the latter 

 little but nuclei remain. The results obtained 

 from the experimental feeding of thyroid by 

 Gudernatsch and others makes it highly prob- 

 able that the non-development of the hind legs 

 in the albinos is due immediately to the 

 atrophy of the thyroid and not to the direct 

 action of the hypophysis, a suggestion which 

 Adler's work upon the tadpole also supports. 



An examination of the gonads shows signif- 

 icant size differences between the normal and 

 albino specimens. In the hypophysectomized 

 animal the development of the sex glands is 

 apparently much retarded and the size corre- 

 spondingly reduced. 



The author in a later and more complete ac- 

 count will describe any changes which may be 

 found in the other endocrine glands and treat 

 of the progressiveness of the changes noted. 

 P. E. Smith 



Anatomical Laboratory, 

 University op California 



effect of grinding soil on the number 



OF MICROORGANISMS 



In connection with a study of the bacterial 

 content of soil, it was found that pulverizing 

 soil in a ball mill seriously affected the num- 



ber of bacteria. This treatment not only 

 reduced greatly the bacteria, but also that 

 of many other microorganisms. In many 

 cases the soil was partially air dry and con- 

 tained clumps which were not easily broken by 

 shaking in a water suspension. Because of the 

 mass of soil particles, it was thought that per- 

 haps grinding would result in a higher count. 

 From the results below, it will be seen that 

 such was not the case. Instead of a gain, 

 there was a loss in number of organisms which 

 was more marked the longer the soil was 

 ground. 



The test was made as follows: Fresh or par- 

 tially air-dried soil, containing not more than 

 10 per cent, moisture, was placed in a ball mill 

 partly filled with large pebbles. The mill was 

 geared so that the porcelain jar revolved at the 

 rate of 70 revolutions per minute. 



TABLE I 



A COMPARISON OP THE NUMBER OP BACTERIA IN 



GROUND AND UNGROUND SOIL 



The following results, shown in Table L, il- 

 lustrate the difference in the number of bac- 

 teria in the ground and the unground soil, as 

 well as the effect of time of grinding on the 

 number of bacteria. Grinding greatly reduced 

 the number of bacteria except in one case, No. 



