134 HOW TO WORK 



fungi. The student should carefully examine specimens of these 

 bodies. Blood corpuscles are readily obtained by pricking the finger. 

 A very thin stratum of the fluid is alone required. By drawing a 

 needle across the thin glass under which the blood corpucles are 

 placed, they may be divided into many smaller globules. This proves 

 that the red blood corpuscles consist of a mass of soft viscid 

 matter, the outer part of which is somewhat hardened. This subject 

 has been fully considered in " The Microscope in its Application to 

 Practical Medicine," p. 169. The sporules of some fungi very closely 

 resemble blood corpuscles, and have been mistaken for them. The 

 common yeast fungus, in different stages of growth, is represented in 

 pi. XXXIII, fig. 211. The blood corpuscles of some animals crystal- 

 lize very readily. The student should place a drop of Guinea pig's 

 blood, under thin glass, and study the changes which occur in the 

 corpuscles during a quarter of an hour or twenty minutes, pi. XXXIII, 

 figs. 213, 216. 



The sloth and the camel, among mammalia, are said to possess 

 nucleated red blood corpuscles, but Dr. Rolleston was unable to verify 

 this observation in an examination he made a short time since. We 

 cannot, however, entirely accept his conclusions, because the blood 

 examined by him was dried on the glass slide. " Note on the Blood 

 Corpuscles of the two-toed Sloth, Cholcepus Didaetylus," Mic. Journal, 

 April, 1867, p. 127, 



Red blood corpuscles of the frog are represented in fig. 214, 

 pi. XXXIII, and in fig. 215, white blood corpuscles of the same 

 animal. 



234. Of the Circulation of the Blood. For studying the circu- 

 lation in the web of the frog's foot, a young frog with a thin web 

 should be selected. The body and one hind leg are loosely bound 

 up in wet rags, the other leg being allowed to protrude. The body is 

 then tied to the frog plate, and a piece of thread having been care- 

 fully tied to two of the toes, the webs may be stretched over the 

 glass at the end of the plate, and fixed in the proper position for 

 observation. A drop of water may then be added, and the web 

 covered with thin glass. 



By careful observation of the circulation, first of all under a low 

 power, and then under a quarter of an inch object-glass most impor- 

 tant and highly interesting facts will be learnt. In cases in which it 

 is necessary to conduct observations on the circulation with the aid of 

 very high powers, it will be found desirable in practice to increase 

 the length of the tube instead of employing object glasses of very 

 high magnifying power. A quarter of an inch object glass may thus 

 be made to magnify as highly as a twelfth, and as the distance 



