CHAP, i.] BLOOD. 29 



crease or decrease of the total number of corpuscles in the body. 

 After a very large reduction of the^ total number of red corpuscles. 

 as by haemorrhage or disease (anaemia), the normal proportion may 

 be regained even within a very short time. 



2] There are reasons for thinking that the urinary and bile- 

 pigments are derivatives of haemoglobin. If this be so, an immense 

 number of corpuscles must be destroyed daily (and replaced by 

 new ones) in order to give rise to the amount of urinary and bile- 

 pigment discharged daily from the body. 



3. When the blood of one animal is injected into the vessels 

 of another (ex. gr. that of a bird into a mammal), the corpuscles of 

 the first may for some time be recognised in blood taken from the 

 second; but eventually they wholly disappear. This of course is 

 no strong evidence, since the destruction of foreign corpuscles 

 might take place even though the proper ones had a permanent 

 existence. 



That the white corpuscles or leucocytes also are continually being 

 destroyed and replaced is similarly probable from the fact that they 

 vary extremely in number at different times and under various 

 circumstances. Most observers agree that they are very largely 

 increased by taking food. Thus during fasting they may be seen 

 in a drop of blood to bear to the red the proportion of 1 in 800 

 or 1000. After a meal this proportion may rise to 1 in 300 or 400.- 

 The mode of origin of the red corpuscles is so fully dealt with 

 in histological treatises and at the same time the subject of so 

 many conflicting opinions, that it will be sufficient to remind the 

 reader that the facts at present in our possession seem to shew 

 that in the adult the generation of new corpuscles takes place 

 chiefly in the red medulla of bones, but also, at all events in young 

 animals, and especially after great loss or destruction of red 

 corpuscles, in the spleen and possibly in other places. In the 

 peculiar capillary mesh-work of the red medulla are found certain 

 corpuscles which differ, among other characters, from the normal 

 red corpuscles (in mammals) by possessing a nucleus, and from the 

 ordinary leucocytes by having their protoplasm impregnated with 

 a certain quantity of haemoglobin. These peculiar intermediate 

 corpuscles appear to be transformed into normal red corpuscles, 

 but the exact mode of transformation, whether for instance the 

 nucleus is bodily extruded from the cell, or broken up within the 

 cell, or whether indeed, as some think, the nucleus and not the 

 whole cell becomes the red corpuscle, is not yet wholly cleared up. 

 Nor are we at present sure whether these peculiar corpuscles 

 themselves arise by a metamorphosis of ordinary leucocytes, or 

 as Bizzozero urges, represent a special class of cells, whose 

 continual existence is ensured by their continually undergoing 

 division. Intermediate cells of this description (which must 

 not be confounded with smaller cells described by Hayem, and 

 called by him haematoblasts, but whose nature is doubtful) have 



