LESSON 23.] CELLS FLOATING IN ANIMAL FLUID. 67 



much as a third larger or smaller than the average. The size of 

 the animal offers no criterion for the size of the blood corpuscle, al- 

 though it is true that they are largest in the elephant of all the mam- 

 malia, he being, at the same time, the largest mammal ; but the pigmy 

 mouse tribe (Fig. 107) possesses corpuscles many times larger than 

 those of the musk deer (Moschus Javanicus). 



385. Much controversy has existed amongst microscopists as to 

 whether the human blood discs contain a nucleus or not. Reasoning 

 from analogy they ought to possess a nucleus, and many observers 

 have a firm conviction that they can plainly detect it. In all the 

 Ovipara it certainly exists, and can be rendered apparent by dissolv- 

 ing the external envelope and setting the nucleus free. A represen- 

 tation of the corpuscles of human blood is given (Fig. 97); the 

 preparation from which the drawing was made 9T 



is dry, and it can be placed in focus, so as to 

 show a very distinct, red colored nucleus (a). 

 Those who deny the presence of a nucleus, at- 

 tribute the effect of color to refraction. 



386. The membrane which forms the cell- 

 wall of the corpuscle is readily permeable by 

 fluids, and under their influence its form is 



easily altered ; treated with water, the liquid Human Blood Cor P U8cles - 

 readily passes into the cell ; firstly the disc becomes flat, then double 

 convex, so that all trace of the nucleated spot is lost ; afterwards it 

 becomes globular, and in the end it bursts the contents (whatever 

 they may be) escaping. But if treated with a thick syrup, or albu- 

 men in solution, their contents will pass out, and the cell-wall assume 

 a shrivelled appearance ; the first effect of this treatment is to increase 

 the concavity, and render the central spot more conspicuous. 



387. It has been stated that the size of the human red corpuscle 

 varies, and according to accurate measurements it appears to range 

 from the l-4,000th to the l-2,800th of an inch ; probably the aver- 

 age is about the l-3,200th. 



388. When inflammatory action exists, the red corpuscles have a 

 great tendency to aggregate and form rouleau (b, Fig. 97); this 

 condition is so certain that frequently when fingers have been pricked 

 to show the blood obtained, to a party of assembled guests, one of 

 them has thus demonstrated the presence of slight inflammatory 

 action. 



389. From a series of experiments made upon the frog's blood, 

 the corpuscles of which are shown in Fig. 98, it appears that the nu- 



