3. A small number of drugs are known to act directly upon the white corpuscles. Quinia reduces their number, and paralyses their movements; Veratria kills them (out of the body). All aromatic oils, resins, and gum-resins, especially Myrrh, are believed to increase their production.

4. We can increase the richness of the blood in red corpuscles, and the richness of the individual corpuscles in haemoglobin, by giving abundant digestible and assimilable food, and by securing the activity of the lacteal tract, which is concerned in their production. Fresh air and sunlight can be secured by change of habits or residence. We can also increase the constituents of the red corpuscles admitted into the system. Iron, which the pharmacopoeia provides in so many forms, directly increases the amount of haemoglobin even in healthy individuals. Carbonate of Potash, in proper combination with Iron, as in the Mistura Ferri Composia or Blaud's pill, unquestionably increases its value. Phosphoric Acid, whether as the Diluted Acid or as the Phosphate of Iron and other bases, is also a reputed blood-restorer. All these substances, and such others as indirectly improve the quantity and quality of the haemoglobin, are known as haema-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, 2K3C6H5O7 + O18 (from haemoglobin) = 3K2CO3 + 9CO2 + 5H1O. 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 Aetheris 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 conditions 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 anaemia; greatly diminished in cholera, where its excretion is excessive. The alkalinity of the plasma is believed to be reduced in rheumatism, from some unknown cause. Uric acid is certainly in excess in gout. In calculous subjects there is apparently some obscure tendency to disturbance of the reaction of the blood, referable to derangement of primary and secondary digestion. Sugar is in excess in diabetes, probably from disordered supply; urea is in excess in Bright's disease, from defective excretion. The white corpuscles are liable to abnormal increase, as in leukaemia, but it is still doubtful whether these are instances of primary disease of the blood.

The diseases of the red corpuscles are certainly few and imperfectly known; practically they may be represented as deficiency, and deoxydation or reduction of haemoglobin. Deficiency of haemoglobin, whether traceable to want of blood as a whole, to poverty of the blood in red corpuscles, or to deficiency of the individual corpuscles in haemoglobin, reduces the oxygenating value of the vital fluid. All the bodily functions become feeble: the patient is weak, dull, sleepy, and suffers from every possible functional derangement, especially shortness of breath.

Reduction of haemoglobin, or, more correctly, of oxyhaemoglobin, is a result of the admission to the blood, in poisonous quantities, of certain substances which we have already mentioned, such as Phosphorus, Arsenic, or Turpentine in poisonous doses. Carbonic Oxide enters into combination with the haemoglobin, whilst the oxygen is expelled from the corpuscles. Hydrocyanic Acid unites partly with oxyhaemoglobin, partly with reduced haemoglobin. Other bodies, such as Sulphuretted Hydrogen, seize upon and combine with the oxygen, leaving the reduced haemoglobin to be dissolved out of the corpuscles and diffused through the blood. Either of these conditions is highly dangerous, the new haemoglobin compound in the first case being with difficulty replaced by oxyhaemoglobin; whilst the reduction and solution in the second case are incompatible with life if they have occurred to any extent.

IV. Natural Recovery

The quantity and functional value of the liquor sanguinis, being but the balance between the income and output of the body, readily return to the normal after disturbance. The same is true of the corpuscles. As long as the disorders of the red corpuscles are of a purely quantitative kind, the restoration of the normal conditions is followed by a return of the blood-elements to their proper constitution. The natural means of recovery are to be found in the shortness of breath and debility which accompanies anapmia, and which compel the patient to spare the blood every possible source of waste; at the same time the increased frequency of the pulse and breathing compensate for want of haemoglobin. Unfortunately there is here as elsewhere a limit to recovery, as when large quantities of a poison, such as carbonic acid, have entered the blood, or when the haemoglobin has been reduced.