June 9, 1922] 



SCIENCE 



625 



III the 3.75 em free-martin the gonad is much 

 less than half the bulk of those of normal 

 males and females of corresponding age. The 

 germinal epithelium (cortex of ovary) is only 

 about one fifth the thickness of that of the 

 normal female of corresponding age and less 

 developed than a female of 3 cm greatest 

 length. The blood of the male has already 

 operated to inhibit growth of the entire gonad 

 and to stop the differentiation of the cortex. 

 The specific male sex-hormone is thus demon- 

 strably present in the blood at this stage. 



Interstitial cells appear in the testis of the 

 normal calf embryo between the stages of 2.7 

 and 3 em greatest length. At the latter stage 

 they are identical in size and histological struc- 

 ture with those of later stages and the adult; 

 they have a continuous history up to adult age. 

 In the female, on the other hand, comparable 

 cells do not appear in the ovary until about the 

 time of birth. 



The following conclusions may be drawn: 



1. The appearance of interstitial cells in the 

 testis at the very time that a male hormone may 

 be demonstrated by its physiological effects 

 (free-martin) is strong evidence that these cells 

 secrete the sex-hormone. 



2. The absence of such cells in the female 

 and the corresponding lack of effect of the 

 female blood on the male twin argue in the 

 same sense. 



3. In the female of cattle sex-differentiation 

 before birth is apparently due to genetic factors 

 exclusively; in the male the genetic factors are 

 intensified by the production of a hormone. 



The detailed data will be published shortly 

 by the authors separately, Mr. Bascom dealing 

 with the interstitial cells. 



Frank R. Lillie 

 K. F. Bascom 

 Hull Zoological Laboratory, 

 The University or Chicago 

 May 18, 1922 



THE EFFECT OF ACID ON CILIARY ACTION 

 AS A CLASS EXERCISE IN pH 



The effects of changes in hydrogen-ion con- 

 centration have received so much attention in 

 the recent literature that it has become desir- 

 able to incorporate some exercise into labora- 



tory coui'ses in physiology which will illustrate 

 the principles by which the p^ of a solution 

 is determined. For the majority of college 

 laboratories "gas chain" apparatus, potentio- 

 meters, etc., are out of the question for student 

 work. The colorimetric method, however, which 

 is very simple and sufficiently accurate for 

 general laboratory problems, can be used to 

 good effect at very little expense. 



For our class in general physiology consist- 

 ing of some twenty students in their second 

 and third college years, we have outlined an 

 experiment on the stopping of ciliary move- 

 ment in the epithelium of the frog's esophagus 

 by acid which has proved most successful. The 

 experiment is in the form of a problem, and 

 is stated thus : "Find the concentration of acid 

 which will stop ciliary action within approxi- 

 mately three minutes." The students work in 

 pairs. A small bit of ciliated epithelium is 

 placed on a slide, and while one student ob- 

 serves this under the low power of the micro- 

 scope, the other places upon the tissue a few 

 drops of acid, and records the time. When the 

 concentration has been found which stops the 

 movement of cilia in three minutes, an indica- 

 tor is added in the correct proportion (Clark, 

 '20, p. 40) and the p^ determined by matching 

 the resulting color with the appropriate color 

 in the color chart. 



When acetic acid diluted with distilled water 

 was used with brom phenol blue as indicator, 

 the following answers were handed in by the 

 class : 



Motion stopped in less than 2 min., p := 3.4, 



2 groups of students. 

 Motion stopped in 3 min., p^j =: 3.5, 6 groups of 



students. 

 Motion stopped in 3% min., p ^ 3.6, 1 group of 



students. 

 Motion stopped in 9 min., y^ = 3.8, 1 group of 



students. 



The agreement between these results is, we 

 think, vei'y good for an ordinary class exercise. 



It should be noted that ordinary distilled 

 water is decidedly acid, pn = ±6.3, and that 

 cilia cease to beat in it within approximately 

 half an hour. In 0.7% NaCl, the beating con- 

 tinues for a day, and in Ringer's solution for 

 three or four days at room temperature. For 



