ANATOMY AND HISTOLOGY OF THE TESTIS 425 



are reduced, but when the animals become active again and spermatogenesis 

 begins, they increase enormously. 



No attempts have yet been made to check them up in a statistical way 

 with other presumably internal secretory tissues, owing, perhaps, to the 

 extreme difficulty of making quantitative determinations. 



Histology 



Arrangement of Cells. In adult human testes the interstitial cells 

 vary considerably in number as between individuals. There is no marked 

 difference between right and left testicles. Interstitial cells occur singly 

 and in groups, which may or may not be related to blood vessels (Fig. 

 1). Sometimes the cells form acinus-like clusters. They are easily 

 identified and may be distinguished from connective tissue cells by their 

 general appearance, as well as by the fact that they do not stain with vital 

 dyes, like try pan blue (Addison and Thorington). 



The Nuclei. The nuclei of the interstitial cells are usually single 

 and spherical, but double nuclei occasionally do occur. Whether or not 

 the double nuclei result from amitotic division, as has been frequently 

 suggested, cannot yet be answered. The nuclei are poor in chromatin and 

 rarely contain distinct nucleoli. Occasionally the nuclear membranes are 

 slightly indented. Karyokinesis is seldom seen in the mature condition. 



Mitochondria. In lower forms, and probably also in man, the cyto- 

 plasm of the interstitial cells possesses an intense affinity for mitochondria! 

 stains, which color them diffusely, unless the differentiation is carried to 

 an extreme. Certain cells in the corpora lutea, suprarenal, and nervous 

 system have the same property. No adequate explanation for the phe- 

 nomenon has as yet been offered, though it has been suggested that it may 

 be due to a slightly acid reaction on the part of the cytoplasm. 



Mitochondria have been investigated in man by Winiwarter (b) and 

 others. They occur in the form of granules and rods, filaments being 

 seldom seen. They are usually distributed fairly evenly throughout the 

 cytoplasm, but may be gathered together in small clusters. The mito- 

 chondria may be stained in fresh living cells, teased out in a dilute solu- 

 tion of janus green, and their relations, as seen in fixed tissues, confirmed. 

 Winiwarter claims to have seen transitions between mitochondria and 

 crystalloids, but does not advance any satisfactory evidence as to their 

 nature. Duesberg describes the coalescence of mitochondria, the appear- 

 ance of vesicles, etc., and interprets these formations as evidences of 

 faulty fixation. 



Centrosomes. The best description of centrosomes in human inter- 

 stitial cells is given by Winiwarter (6). They may be either spherical or 

 rodlike. When the nuclei are indented, the centrosomes are often found in 



