on Ihe Vitality and Life of dehns, c^l 



!iiay fay, the mod impatient irritability is obferved. But 

 Vvhy does a ftimuliis fo powerful as caloric, in a certain dofe, 

 extingLtifli the life of the aduh, without altering, or, at leaft^ 

 without alterincT much, the life of the fame animal ftill 

 in embryo? 4 



We have as little knowledge refpe6ling the action of gafes, 

 odoriferous Or narcotic effluvia, miafmaia. Sec, In a wordj 

 there would be many agents to examine by applying them 

 to animals externally; but I fhall confinfc mylelf to an ex- 

 amination of the principal ones, and in the fimpleft and 

 eafielt manner, ift, Has light any aftion on the embryo 

 Hill contained in the egg? Is its a6lion ufeful or prejudicial 

 to it? 



I'o decide this queftion, I took oti the 5th of December 

 1796, four glafs jars of the fame fize, two of which I co- 

 vered with a coating of black wax, and I put iiito ,each an 

 equal quantity of the eggs of the phal^na difpar Linn. I 

 clofed each of them \vith a pierced ftopper, through which 

 I iiifcrted a bent tube, coated in the fame manner, to 

 inaintain a free communication between the internal and 

 external air, preventing, as much as poffible, the pafTage of 

 light into the coated ]ars. I then placed in a northern expo- 

 fure a black jar and a tranfpareilt one in a lituation where 

 the fun had no accefs; the other two wereexpofed to the 

 fouth, that is to fay^ to the moil powerful a<Slion of that 

 luminary. 



In both, places the greateil cold during winter was -f- i8^° 

 Fahrenheit, and the greateft heat towards the north, that at 

 the period of the birth of the caterpillars, was + 66", while 

 towards the fouth in the fun it was as high as + 109^-°. 



On the 20th and 2l(l of April 1797, when the eggs of 

 thefephala^noe were not hatched in the fields, on vifiting my 

 black jar towards the fouth, I found the greater part of the 

 eggs already hatched; the fmall caterpillars had aCcended to 

 the highell part of the neck of the jar, to which they had, 

 no doubt, been attra6ted by f()nie rays of light that, not- 

 withftauding mv precautions, penetrated through the, bent 

 luoe. On infpe<Sling at the fame time the other jar towards 

 Vpi.. IX. " H U the 



