62 BASIC METHODS FOR EXPERIMENTS 



Meves' solution as shown in the table given above contains 

 half the amount of chromic acid and one fifth to one tenth less of 

 glacial acetic acid than the Flemming. That these are impor- 

 tant differences, can be shown by fixing cells of kidney, pancreas, 

 small intestine of the rabbit, guinea pig and rat; eggs of various 

 invertebrates, including those of cephalopods and of Crustacea 

 and eggs of bony fishes and blastoderms of chicks; testis cells of 

 Protenor belfragi, Anas a tristis (Hemiptera), Gryllus, Romalea 

 and other Orthoptera as well as Paramaecia and other Protozoa. 

 In every case it has been my experience that the Meves with less 

 chromic acid and acetic acid and with the lesser amount of osmic 

 acid gives superior fixation. 



With Meves as I use it nuclei and chromosomes are beauti- 

 fully fixed. The configuration of the mitotic figure observed in 

 the living Qgg is preserved almost without change. In addition, 

 mitochondria are so well fixed that one need not employ special 

 stains to reveal them; they show up perfectly with haematoxylin, 

 as we shall see later. The yolk-spheres are preserved intact 

 and the oil is not dissolved out. These points one can determine 

 for oneself by comparing the structure of these bodies In a fixed 

 preparation with their structure in a living egg, like that of a 

 nereid worm, in which the oil and yolk are clearly revealed in 

 the living state. In Flemming the oil is dissolved and the yolk 

 is badly fixed; the mitochondria are not preserved. With refer- 

 ence to the oil-drops, a centrifuged echinid tg^ makes a striking 

 example, for after the modified Meves fixation the oil-drops 

 constituting the gray cap at one pole of the living egg can 

 actually be counted in the sectioned egg. 



The cytoplasm of marine eggs with which I am familiar is by 

 and large well fixed by any one of a number of fixing solutions. 

 However, a fixative, as is the case with most, that dissolves out 

 the oil and distorts the yolk-spheres even when these are not 

 dissolved, is apt to cause some change in the cytoplasm. Even 

 in centrifuged eggs, in which the cytoplasm (ground-substance) 

 is separated as a clear zone, the dissolution of the cytoplasmic 

 inclusions undoubtedly has some effect. It is, therefore, better 

 for investigation on the cytoplasm Itself to employ a fixative 

 that does not have these deleterious effects on the inclusions. 

 Also, it is reasonable to suppose that a fixative that preserves all 



