441 
OK INSECT OF ITCH AND MANGE. 
of the same species ; and if, farther, that the manner of living in 
these insects is the same, it may be concluded that the patho¬ 
logical state of the skin in the itch and the mange would be very 
similar. But if these facts are proved, there still remains 
another and a very important question to be decided. 
Are the acari the consequence or the cause of the itch and 
mange, and are they invariable or only incidental ? 
The usual appearance of the disease in question is caused by 
a peculiarly acrid fluid, which has been considered by some per¬ 
sons to be the most extensive cause of cutaneous disease. The 
diseases which arise from these humours are caused partly by 
bad nourishment, partly by want of nourishment, or by unclean¬ 
liness, or infection, or they are hereditary. The origin of the itch 
blisters and mange sores is only the consequence of a more highly 
developed acidity, or sometimes these eruptions constitute the 
crisis of some other disease ; and if acari are found in the itch 
and mange, they may be only parasites who are nourished by 
the fluid contained in the blisters. 
This is not the place to i notice all the opinions that have 
been held on the subject of the itch and mange, and I deem it 
sufficient for the present purpose to make the following obser¬ 
vations :— 
1. It has never been clearly proved that the itch or the mange 
can be produced by bad or by scanty food ; and even when the 
disease appears cotemporaneously with the existence of these 
agents, it is well to examine carefully whether any other means 
of infection have been in the way. 
2. Walz maintains that mange (and especially in sheep) is 
produced by damp ground, or standing water, which cause a 
softening and relaxed state of the skin. This is the only dis¬ 
eased state of the skin in which it is believed that the acari 
can spontaneously develop themselves in the organic matter. 
3. There is never any peculiarly increased power, or any 
acidity of the humours to be observed at the beginning of itch 
or mange; but when the disease has spread itself over a great 
part of the body, and thereby disturbed the functions of the 
skin, the consequence will be a diseased state of the nutritious 
juices, and therefore of the humours. 
4. The return of the itch or mange which is occasionally seen 
after the use of certain medicines, and is eagerly quoted as a 
proof against the theory of insects causing the disease, and 
considered as a proof that these complaints are diseases of the 
humours, ought rather to be considered as exceptions to the 
general rule. 
5. It has been |)rovcd by wcll-authcnticatcd experiments, 
