DRUGS WHICH ACT ON THE BLOOD 449 



these substances, and such others as indirectly improve the 

 quantity and quality of the haemoglobin, are known as hsema- 

 tinics. 



Arsenic, Phosphorus, and perhaps other metals combine 

 with the haemoglobin, partially reduce it, or otherwise interfere 

 with its constitution or quantity, so as to impair the oxygenating 

 power of the corpuscles if given in full doses. Citrates and 

 Tartrates have a peculiar deoxidising effect on the blood, 

 being converted in part into carbonates at the expense of the 

 haemoglobin, thus, 2K 3 C G H 5 07 + Oi 8 (from haemoglobin) 

 3K 2 C0 3 4- 9C0 2 4- 5H 2 0. Lead reduces the number of the 

 red" corpuscles, but probably indirectly, by interfering with 

 digestion. Iodine and Sulphur (Sulphides), Turpentine, and a 

 few other drugs, such as Diluted Hydrocyanic Acid, reduce the 

 oxy-haemoglobin of the corpuscles, but only after excessive 

 doses, so that in this respect they may be regarded not as 

 drugs, but as poisons, and will be noticed in the next section. 

 The Nitrites of Amyl and Soda, and Spiritus JEtheris Nitrosi 

 convert part of the haemoglobin into met-haemoglobin, but only 

 when given in excess. On the other hand, Alcohol and Quinia 

 bind the oxygen more firmly to the corpuscles, and thus reduce 

 oxygenation. Nitrous Oxide gas acts indirectly on the corpuscles 

 by taking the place of oxygen, but does not chemically combine 

 with the haemoglobin. It is manifest that the methods of 

 venesection and transfusion will influence the corpuscles as 

 well as the plasma. 



III. PATHOLOGICAL RELATIONS. 



As was mentioned in the introduction, the morbid con- 

 ditions of the plasma are chiefly secondary ; that is, caused by 

 disorder either of the organs from which it draws its supply 

 the digestive organs and liver, or of those by which its 

 products leave the body, especially the lungs and kidneys. 



Thus excess of blood, which constitutes one kind of 

 plethora, is referable to indulgence in food, combined with lazy ' 

 habits. The opposite condition, anaemia, or deficiency of blood, 

 is a very common disorder, which may arise from an endless 

 variety of causes, whether of the nature of want (insufficient 

 food or imperfect digestion) or of waste (excessive work, growth, 

 exhausting diseases, or haemorrhage). The constituents of the 

 plasma are no doubt often disordered, but this subject is still 

 obscure. The albumins are deficient in anaemia. Carbonic 

 acid increases in respiratory difficulty. The water of the 

 blood is increased in amviuia ; greatly diminished in cholera, 

 where its excretion is excessive. The alkalinity of the plasma 

 is believed to be reduced in rheumatism, from some unknown 

 2 D 8 



