314 DR DAVY ON THE QUARANTINE CLASSIFICATION OF SUBSTANCES, &c. 



a minute, and then examined them with a microscope. Traces of the animal mat- 

 ter in each instance were distinctly perceptible ; in two, indeed, it was not per- 

 ceptibly diminished by the immersion. The two were the cerumen of the ear, and 

 that soiling matter from the hand, or any other part of the surface of the body, 

 which, as is well known, dulls by contact any polished surface. Those of which 

 traces only remained were saliva dried, the finest pellicle, and a stain of blood. 

 The difference noticed between these animal matters, as regards their appearance 

 after immersion, no doubt depends on the nature of the particular substances. 

 Saliva and blood both contain matter soluble in water, which will be removed by 

 its action ; whilst the epithelium fragments in the one, and the fibrin in the other, 

 will remain, being insoluble. In the other two instances of the cerumen of the 

 ear and the soiling matter, the excretion from the skin, the material of each being 

 in most part insoluble in water, it could not be expected that immersion for so 

 short a time should have any visible effect. I have found, indeed, that glass 

 dulled by having been applied to the upper eyelid, or by being held between the 

 thumb and fore-finger, or pressed against other parts of the body, may be im- 

 mersed in water several hours, even days, without losing its peculiar appearance 

 when placed under the microscope, an appearance it seems to owe to sebaceous 

 or oily matter mixed with epithelium scales in constant process of excretion and 

 separation. 



These few instances, which might be easily multiplied, may suffice to illus- 

 trate the danger lurking under the classification commented on, and how, if it be 

 based erroneously, as I have endeavoured to show, it undermines altogether, and 

 renders, as before said, worse than useless the other parts of the system of qua- 

 rantine as at present followed. 



MuRRAYFIELD HoUSE, NEAR EDINBURGH, 



March 31. 1842. 



