49 



very similar, differing chiefly in the degree of organisation or 

 vitalisation to which they have respectively attained. The 

 white may be regarded as the first step towar.ds the formation of 

 the more highly endowed red fluid. In only one vertebrate — 

 viz., Branchiostoma, or Lancelet, is the circulating fluid white. 

 The two fluids circulate in distinct systems of vessels. The 

 red fluid, or that one which is usually referred to when the 

 term blood is used, exists in man to the amount of about one- 

 tenth the weight of the body. The mistakes which have been 

 made, and the difficulties which have been encountered in the 

 determination of the exact quantity of blood in the body, offer 

 a good illustration of the necessity for proceeding in all phy- 

 siological inquiries according to well-devised philosophical 

 methods. The lecturer then proceeded to describe the consist- 

 ence, colour, odour, taste, temperature, reaction with litmus 

 paper, &c, of the blood ; the phenomena accompanying its 

 coagulation ; the method of separating and estimating the 

 quantity of the corpuscles ; the size and shape of the red 

 blood corpuscles in man and the lower animals. The following 

 statements were then made : — In man the diameter of a red 

 blood corpuscle averages i-35ooth of an inch, and its thickness 

 about one-fourth of that magnitude. As a rule, the red blood 

 corpuscles of quadrupeds are smaller than those of man — the 

 elephant, in which they are 1-2700 of an inch being an excep- 

 tion. The Napu musk-deer has very small corpuscles ; their 

 diameters seldom exceeding i-i20ooth of an inch. In reptiles, 

 on the other hand, the corpuscles are comparatively large, 

 being as great as 1.387th of an inch in the Proteus. A cubic 

 inch would contain 70,000,000,000 human red blood cor- 

 puscles ; that is to say, eighty times the population of the 

 globe. White corpuscles are found in the blood in the pro- 

 portion to the red, of 1 to 226 in boys ; in men, 1 to 346 

 and in old men, 1 to 381. An interesting phenomenon 

 presented by the white blood corpuscles is the remarkable 

 changes of form they exhibit when examined under the micro- 



G 



