58 ALICE M. BORING AND RAYMOND PEARL 



of temperature. But none of these precautions gained any bet- 

 ter separation of the chromosomes. The Gilson's solution gave 

 clearer fixation than either cold or hot Flemming or Hermann. 



Very small pieces of the testes of some of these same birds 

 were put into aceto-carmine and allowed to stay indefinitely. 

 When examined later and spread one layer of cells thick under 

 a coverglass, the chromosomes were sharper and clearer than 

 in any of the sections of the material so carefully fixed. If 45 

 per cent acetic acid, saturated with carmine, gives good results, 

 it seemed possible that other closely related organic acids or 

 other concentrations of acetic acid might give even better chro- 

 mosomal pictures. Consequently 45 per cent formic acid, 45 

 per cent butyric acid and 40 per cent chloracetic acid were tried. 

 The butyric acid is too heavy and does not penetrate the cells at 

 all. The formic acid fixed the cells well, but did not carry the 

 stain in as well as the acetic. Of the different percentage so- 

 lutions of the acetic acid tried, the 5 per cent did not either fix 

 or stain well, the 100 per cent gave good sharp fixation, but 

 would not dissolve enough carmine to stain properly. So noth- 

 ing was found to improve on the 45 per cent aceto-carmine. Fig- 

 ures 86-91 are some of the aceto-carmine preparations. 



Finally smears were made exactly as Guyer made his for the 

 Langshan cocks. The testes were taken from an old bird in its 

 second year. The smears were fixed in Bouin's solution and 

 stained in iron hematoxylin. The black and white of the iron 

 hematoxjdin preparations is especially favorable for both draw- 

 ing and photographing, and the smears are much better than 

 the sections stained in iron hematoxylin. So figures 1 to 85 are 

 all made from smear preparations. 



OBSERVATIONS 



» 



This paper does not attempt to work out a continuous detailed 

 history of spermatogenesis in the Barred Plymouth Rock. A 

 glance at the photographs and drawings on plates 1 to 6 will 

 show that such a history would require a large amount of imag- 

 ination. These plates show, however, that in some of the di- 

 viding cells, a chromatin mass appears separate from the rest 



