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8 June, 1908.] Elements of Animal P/ivsiology. 349 



appear circular, but looked at end-on they are dumb-bell shaped. Mam- 

 rrialian corpuscles do not possess nuclei and cannot be regarded as living ; 

 in fact there is evidence to show that they are continually being broken 

 dov\rn and replaced by fresh ones in the marrow of certain bones. Their 

 size (diameter of the disc) varies slightly with different mammals and 

 probably also in the same species. The following table gives approximately 

 the diameter of a number of types : — 



Man ... .. ... TpvjHj inch. 



I>og 



Pig and Ox ... 



Horse 



Sheep 



The number of corpuscles present is usually stated in terms of the 

 number present in a cubic millimetre* of blood. Thus — 



Horse, 6,500,000, — 8,000,000 corpuscles per cubic millimetre. 



Man, ox, pig and dog, about 5,000,000 corpuscles per cubic millimetre. 



Goat, 9,000,000 — 10,000,000 corpuscles per cubic millimetre. 

 The red corpuscles are composed of an external envelope of lipoid within 

 Avhich IS a meshwork of protein holding in its spaces the red colouring 

 matter of the blood or iiamoglobin which constitutes o\"er 30 per cent, of 

 the weight of the corpuscle. Haemoglobin is a complex protein containing 

 iron, and seems to be present in the body for the sole purpose of 

 carrying the oxygen and part of the carbon dioxide. The red corpuscle 

 may therefore be looked on as a boat for the transfer of the two blood 

 gases, and this propertv it possesses through its haemoglobin content. 

 When haemoglobin is linked to oxygen, forming oxyhcemoglobin, its colour 

 is bright red ; if uncombined with oxygen (simple ha:moglohin) its colour 

 is bluish-purple. Hence the blood leaving the lung and that in the arteries 

 (arterial blood) is red, whilst that leaving the tissues (venous blood) 

 is bluish-purple. When red corpuscles are placed in water or in a 

 salt solution of less than the proper concentration, they swell up and 

 burst, liberating the haemoglobin into the plasma. If placed in a salt 

 solution stronger than the blood they shrink and crinkle at the edges. 

 Anything which dissolves or breaks up lipoid (chloroform, ether, &c. , and 

 certain toxic enzymes) will destroy the integrity of the corpuscle and liberate 

 the haemoglobin ; and it is important to note that haemoglobin, thus libe- 

 rated, acts as a foreign body, is incapable of carrying the gases properly, 

 and is promptly turned out of the blood by the kidney. The red cor- 

 puscles, as has been stated, are elastic. They pass with ease through the 

 pores of fine filter-paper and can be forced thrO'Ugh tubes or apertures of 

 smaller calibre than their diameters. 



The WHITE CORPUSCLES, unlike the red. are nucleated living cells, 

 some of which move to and fro in the plasma and are capable of passing 

 through the walls of the smallest blood-\essel. The number of white cells 

 Ji much less than that of the red ; in man, for one white, 500 to 600 

 red can generallv be found. There are several varieties of white corpuscles, 

 and it is probable that they may have different functions. The most 

 numerous sort are endowed with the power of attacking and digesting 

 bacteria just as an amoeba can digest a particle of food. If bacteria get 

 lodged in a tissue the white cells throng to the spot and a fight for life 

 or death ensues. What is known as pus or matter is most probably a col- 

 lection of white cells which have been exhausted if not killed in the 

 struggle. This contest between the white cells and intruding bacteria is 



* A cubic millimetre is approximately one-fiftieth of the \olume of a drop of water. 



