REPORT OX THE LAWS OF CONTAGION. iS 



culiar*. When we add to these arguments, that the perversion 

 of a vital process, such as that of secretion, occasions, in at 

 least one decided instance {rabies canina), the formation of a 

 poison, by an organ which commonly secerns a bland and harm- 

 less fluid, the weight of evidence must be allowed greatly to 

 preponderate in favour of the opinion, that all morbid animal 

 poisons are the results of vital operations; and that chemical 

 changes, if concerned at all^ are under the control of the vital 

 principle. 



X. Among contagious poisons, there are some that exist in a 

 visible and tangible state, generally in that of liquids ; others 

 are not at all perceptible by our senses, and are known to us 

 only by their efffects. The liquid poisons are efficient, only when 

 applied beneath the cuticle, or to parts where the cuticle is very 

 thin, or to the surfaces of mucous membranes ; and if imme- 

 diately and completely washed off, they inflict no injury. The 

 action of some of those poisons, of siphylis for instance, does 

 not necessarily extend beyond the part to which they are ap- 

 plied. Other poisons, when inserted or inoculated, act locally 

 in the first instance, and afterwards give rise to general febrile 

 excitement, which is necessary to the formation of fresh poison 

 in the inoculated part, or in the system. After inoculation for 

 smallpox, the constitutional disturbance is generally well 

 marked ; in cowpox, often so faintly as to be scarcely distin- 

 guishable ; yet even in the latter, some degree of general fever 

 seems to be essential to the perfect state of the pustule f. It 

 is only at this period of full development (called the time of 

 maturation) that the fluid contents of the pustule, (which in 

 the cowpox is limpid, in smallpox purulent,) can be depended 

 upon for producing its appropriate effect. Before maturation, 

 the fluid is inert ; after that period, it is sometimes effete, and 

 sometimes produces a modified disease;!:. All attempts to ex- 

 cite smallpox or cowpox, by inoculating with the blood or 

 with any other animal fluid, have been unsuccessful §. 



XI. When the liquid animal poisons are kept in a moist state, 

 at temperatures not exceeding those of a warm atmosphere, they 

 undergo spontaneous changes which materially affect their spe- 

 cific properties. Variolous matter, thus negligently preserved, 

 has been known to produce a train of symptoms resembling 

 those of smallpox, but yet giving no security against the return of 



* The odours attending tlie plague, smallpox, and Asiatic cholera are in- 

 stances. 



t Jenner, Inquiry, &c., 4to, 1798, p. 71. 

 X Jenner's Further Observations. 

 § Darwin's Zoonomia, § xxxiii. 2, 



