4 CALIFORNIA ACADEMY OF SCIENCES. 



lute alcohol, others in formaline. But notwithstanding- 

 the different conditions of the hosts, the protozoa did not 

 show any prominent difference in structure, the caryo- 

 plasm only being less distinctly stained in the alcoholic 

 specimens. I am therefore satisfied that the structure here 

 represented and figured is the real one. This I believe 

 with the more confidence as Beddard has shown that the 

 protozoa — Gregarina of Perichgeta — do not generally 

 change their form and structure, even when attacked by 

 powerful reagents. Much of the success in observing- 

 protozoa depends upon the staining, especially so in this 

 form, which was not greatly sensitive to the common 

 stains of heematoxylon, methyl green, safranine, etc. 

 After having tried a dozen or more stains at my disposal^ 

 I found the following method to be superior to any other^ 

 and to give by far the finest nuclear images: 



1. Staining of the hosts in toto in very weak Dela- 

 field's hgematoxylon or in Ehrlich's ammonia haematoxy- 

 lon. 



2. Hardening and sectioning in paraffine. 



3. The slide fixing consisted simply of distilled water 

 or of formaline and gelatin (^ per cent.) in water. This 

 fixing is used as follows : 



1. Cover the space of the cover -glass on the slide 

 with several drops of the fixing, so that the sections will 

 float. 



2. Warm gently over a plate until the paraffine be- 

 comes slightly transparent, but not so long that it be- 

 gins to melt. If it melts, the sections shrink at once and 

 spoil, but if just heated sufficiently they stretch out, even 

 if ruffled by the knife. 



3. Let the fixing harden in the air during at least four 

 hours, or better, during the night. Sections heated this 

 way never loosen, and are always straight. They should 



