PLATE 3 



EXPLANATION OF FIGURES 



1!) Pilot ()<;ra])li of a section of testis of adult woodchuck with interstitial 

 cells at a maxinuim; April 29; reduced body weight 2850 grams, of which one 

 testis constituted 0.106 per cent. Carnoy's fixer; 4 ix thick; iron hematoxylin. 

 X 20. The + is placed on a large nodule of interstitial cells which are especially 

 rich in fat. Lumen of tubules open. 



20 Photograph of section of testis of adult woodchuck with interstitial cells 

 beginning to atrophy; July 10; reduced body weight 2825 grams, of which one 

 testis represents 0.038 per cent. Testes still scrotal. Carnoy's fixer; 4 /^ thick; 

 iron hematoxylin. Tubules no longer open. To be compared directly with 

 figure 15. 



21 Retouched photograph of section of testis of same animal as in figure 20. 

 Modified Zenker's fluid; 4 ^ thick; copper hematoxylin. X 527. Central cyto- 

 plasm still contains numerous fine granules (lipoid) in addition to pigment. 

 To he cnmnared directly with figure 17. 



22 Photograph of section of testis of same animal as in two preceding figiu-es. 

 Meves' fixer; 4 m thick; unstained and uncovered. X 129. A number of large 

 globules of fat are still left in the interstitial cells. To be compared directly 

 with figures 18 and 14. 



23 Photograph of section of testis of adult woodchuck just after atrophy of 

 interstitial cells; August 5; reduced body weight 3190 grams, of which one testis 

 represents 0.016 per cent. Testes abdominal. Carnoy's fixer; 4 ju thick; iron 

 hematoxylin. X 129. Interstitial cells numerous but greatly reduced in size. 

 Tubules contain many spermatocytes. 



24 Retouched photograph of above section under higher magnification. 

 X 527. In addition to numerous ordinary interstitial cells, now rich in pigment 

 but greatly reduced in size, there are four newly formed 'pigment cells' easily 

 distinguishable by their large size, darker color and numerous large pigment 

 granules. 



25 Photograph of a portion of the section immediately following under 

 higher magnification. X 527. A group of newly formed 'pigment cells' as they 

 appear after being acted upon by osmic acid. Only colored plates could do 

 justice to their appearance as seen when the pigment is unstained such as occurs 

 after Carnoy's fixer and hematoxylin and eosin. Carnoy's fixer tends to make 

 them more irregular in outline as may be seen by comparing this figure with 

 figures 4 and 5, all of which are from sections of the same animal. 



26 Photograph of section of testis of this last animal; Meves' fixer; 4 m thick; 

 unstained and uncovered. X 129. The osmic acid darkens the pigment gran- 

 ules of the interstitial cells and blackens the fatty globules in the tubules as 

 well as ordinary adipose cells, which now are very numerous. The hirge newly 

 formed 'pigment cells' stand out prominently. There is a striking absence of 

 fat globules in the interstitial cells. Compare with figure 18. 



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