220 OF THE BLOOD. 



eliminated from the system. But there is this peculiarity in the action of many 

 of the poisons in question, that they have the power of multiplying themselves 

 within the body ; thus, for example, when smallpox has been communicated by 

 the inoculation of an excessively minute portion of the virus, hundreds or 

 thousands of pustules are generated, each of them charged with a poison equally 

 potent with that from which they originated. It is to this multiplication, that 

 the extension of zymotic diseases, by communication between individuals affected 

 with them and healthy subjects, is chiefly due ; and the question of the " con- 

 tagion" or "non-contagion" of any particular disease of this class, is, therefore, 

 essentially that of the multiplication or non-multiplication of the poison in the 

 human body. This multiplication of certain zymotic poisons is a yet stronger 

 point of analogy to the action of ferments, than that which is afforded by the 

 violence of the changes they induce, when compared with the amount in opera- 

 tion. Some of these poisons are of such potency that, in however minute a 

 quantity they are introduced, they will change the whole mass of the blood in a 

 few minutes; and will act indiscriminately on all individuals alike; this is the 

 case, for example, with the venom of serpents. On the other hand, there are 

 many (as already remarked) which seem to require the presence of some special 

 fermentable matter in the blood ( 210). And between these might probably 

 be established a regular gradation from those most " pernicious' 7 forms of 

 malarious poison which derive their potency from the intensity of vegetable de- 

 composition under the influence of a high temperature, and those " malignant" 

 types of typhoid poison which owe their special intensity to animal putrescence 

 engendered by filth and overcrowding, both of these attacking a very large pro- 

 portion of those who are exposed to them to those milder forms of zymotic 

 poisons, which, though derived from the same sources with the preceding, act 

 with so much less of uniformity upon different individuals, that we can scarcely 

 fail to recognize, as a " predisposing cause," or rather as a necessary concurrent 

 condition, the presence of some readily-decomposable matter in the blood. The 

 long-continued action of these poisons, in their milder forms, seems itself capable 

 of inducing this condition; thus, a healthy person who settles in an aguish 

 country, may remain free from intermittent fever for a considerable time, but 

 his health gradually deteriorates, and at last he becomes the subject of the dis- 

 ease, which would have much earlier attacked him if his blood had been brought 

 into the a fermentable" state by irregularity of diet, over-exertion, &c.; and the 

 same may be observed in the case of those long exposed to the poison of typhoid 

 or other fevers, which especially locates itself in animal miasmata, if not actually 

 engendered by them. 



215. In some of the diseases of this class, the change in the qualities of the 

 blood produced by the introduction of the poison, is such as to give it a morbid 

 action on certain organs or tissues only; their phenomena in this respect cor- 

 responding with those of ordinary poisons, and of the toxic diseases previously 

 noticed. Such may be said of hydrophobia, vaccinia, gonorrhoea, primary 

 syphilis, &c., in which the general functions of the body are disturbed chiefly 

 or solely through the local disorder. But, in other cases, we find that the con- 

 tamination of the blood is such as to produce more or less disturbance in all the 

 functions; as we especially witness in the severer forms of fever, in poisoning 

 by venomous serpents, &c. Even in this last class of cases, however, a special 

 determination to one organ or system is frequently obvious; and this may either 

 be so constant as to be characteristic of the disease, which is the case with the 

 skin affection in the Exanthemata ; or it may be chiefly directed by the previous 

 condition of the patient's system, that organ or tissue (amongst those on which 

 the poison is capable of acting) being most affected whose previous nutrition was 

 least healthy, as appears in the variety of local affections that are developed 

 during an epidemic Influenza. This local determination may frequently be 



