170 SHEEP DISEASES : 



less, while others, when in bulk, are of a red colour, they are 

 distinguished respectively as white (leucocytes) and red cells. 

 The former of these are the larger, and they are endowed with 

 the power of motion in a limited degree and of actively altering 

 their shape. The latter are much smaller and are practically 

 devoid of the power of motion ; they are believed to be the highest 

 stage in the development of the white cells. 



Both these bodies are absolutely necessary in the blood, and 

 to the white cells is now ascribed a function which, until recently, 

 was only suspected, viz., the function of destroying injurious 

 organisms, such as the germs of disease — devouring them, in 

 fact — and of removing dead matter from the tissues ; they are 

 the scavengers of the system, and are as voracious as jelly-fish, 

 closing over the object of their attack and digesting it, or all of 

 it that is capable of being digested, and ejecting the remainder 

 into the blood stream. By their agency, too, the solid parts of 

 the blood — even the red cells — are removed from the tissues 

 when that fluid is poured out into them as the result of an 

 injury or in consequence of disease. If, in other words, an indi- 

 vidual is unfortunate enough to get a " black eye," these little 

 bodies set to work, and, by breaking up and removing the red 

 cells, upon which the colour of the bruise is dependent, they 

 restore the damaged tissues to their original condition. More- 

 over, the white cells rush into the breach whenever a wound is 

 inflicted and not only preserve the exposed tissues from the 

 action of injurious organisms but supply all the means by which 

 the breach is filled up. 



The red cells have equally as important, and even more im- 

 portant, an office to fulfil. They are the means by which oxygen 

 is carried to the tissues for the purpose of oxygenation or decar- 

 bonisation. They are, in other words, the conveyancing media 

 of the gas (oxygen) necessary for the purpose of burning up the 

 excess of hydrocarbons and carbohydrates, thus getting rid 

 to a large extent of effete and injurious material, and of keeping 

 up the animal heat. The actual agent by which their oxygen- 

 conveying function is performed is iron, and it is upon this 

 element also that the cells are mainly dependent for their red 

 colour. Deficiency of iron means deficiency in oxygen, and the 

 blood assumes a dark colour — becomes venous, instead of being 

 a bright red or scarlet colour, as in arterial blood. 



The existence of a third corpuscle is now recognised by many 

 physiologists, but to the character and functions of this I need 

 not allude in detail, further than to say that it is believed to be 

 the originator of the other cells ; hence it was called by Hayem 

 a hcematohlast, or blood-former. 



That the blood is possessed of vitality is shown by its power, 

 on withdrawal from the vessels, of undergoing coagulation — a 



