308 DR DAVY ON THE QUARANTINE CLASSIFICATION OF SUBSTANCES, 



tine is now only in process of being introduced From all the information I have 

 been able to collect, it would appear that no accurate method has been employed 

 in determining the non-susceptibility of even any one article in regard to contagion, 

 much less so many and so different. Persons officially employed, who have de- 

 fended the classification, have referred to accumulated experience, without being 

 able to mention any trials, any experiments, any precise observations, on which 

 the inquiring mind can rest with satisfaction. The fact, I believe, is, that the 

 classification, which is almost coeval with the establishment of lazarettos, was 

 made during a time of panic, from vague considerations of the qualities of sub- 

 stances, in ignorant times, and by men unqualified, by the then imperfect state of 

 knowledge, to arrive at accurate conclusions on a subject, as a matter of inquiry, 

 of more than ordinary difficulty ; and that their dicta gaining force with age, which 

 has been called experience, have become laws, and venerable, and almost sacred 

 as such. 



In the absence of all precise experiments, it may be worth while to consider 

 whether, taking into account the qualities of the substances pronounced to be non- 

 susceptible, they are likely to be so in reality. Three of the more important ones 

 may be selected on which to fix the attention, viz. metals, wood, and glass. 



From what is known of the properties of either of these, it must be admitted, 

 I apprehend, that they are totally destitute of all power, either of repelling the 

 matter of contagion, or of destroying it, or, if it be adhesive, of preventing its 

 adhesion. Glass and wood are incapable of effecting any alteration in the com- 

 position of animal substances ; and the same remark applies to most of the metals. 

 Glass and wood, it is well known, are the substances chiefly employed for the 

 purpose of preserving and transmitting vaccine lymph. On wood or glass per- 

 fectly dried, or in glass tubes, in its liquid state, hermetically sealed, vaccine 

 lymph has been preserved many months, and has been transmitted to distant 

 countries. Reasoning from analogy, it seems highly probable, that using the 

 same substances, and the same methods, other contagious matters, not excepting 

 the contagious matter of the plague, might, with equal certainty, be preserved 

 and transmitted. 



It would be a superfluous labour and waste of time to offer remarks on all 

 the different articles generally classed under the head of non-susceptible. Ex- 

 cepting a very few of a doubtful nature, as the alkalies, quicklime, and certain 

 salts, they appear all to come under the same category in relation to the matter 

 of contagion, as glass, or wood, or metal, being neither repellant of it, destructive, 

 nor preventing its adhesion, that is to say, judging from analogy, in the absence 

 of positive experience. 



Let us now turn our attention to the class of substances called susceptible. 

 They are principally the following : 



1. Wool, hair, and skins of different animals ; feathers ; animals, whether dead 



