214 DISEASES OF INSECTS. 
it is a malady of no great importance. Lastly, some- 
times the mulberry leaves have a gummy rather acrid 
secretion, which purges the silkworms; their excrement 
is no longer solid ; they become weak and languid ; and 
if the secretion is abundant, their transpiration is impeded, 
and at the time of moulting they are become so feeble as 
to be unable to cast their skin a . 
In the case of many caterpillars of Lepidoplcra that 
died, Bonnet found by dissection that the disease was 
remotely occasioned by a diarrhea, which taking place 
immediately before they became pupae, prevented the 
inner membrane of their intestines from being rejected, 
as it would have been if no extraordinary cause had 
prevented it, attached to the hard excrement. He found 
this membrane converted into a jelly occupying great 
part of the stomach, which he conjectured was the proxi- 
mate cause of their death b . 
To conclude this head — spiders are reputed to be sub- 
ject to the stone : I do not say Calculus in Vesica ; but 
we are informed by Lesser that Dr. John Franck hav- 
ing shut up fourteen spiders in a glass with some vale- 
rian root, one of them voided an ash-coloured calculus 
with small black dots . 
II. I now come to that class of diseases which appears 
to prevail almost universally amongst insects — I mean 
those resulting from the attack of parasitic enemies. 
Thus millions and millions annually perish before they 
have arrived at their perfect state. Diseases of this kind 
proceed either from vegetable or animal parasites. I shall 
begin with the first, which will not occupy us long. 
i. As insects pass often no small portion of their life 
n Latr. Hist. Nat. xiv. 163—. A r . Diet. (VHist. Nat. iv. 134—. 
b CEtevr. ii. 48-. c Lesser L. ii. 121. 
