364 PHILOSOPHY OF ZOOLOGY. 
Urinary concretions have likewise been detected in the 
horse, ox, sow, dog, rabbit, cat and rat. In none of these, 
however, has any trace of uric acid been detected. In all 
of them the base is lime, or magnesia, united with phospho- 
ric, carbonic, or oxalic acids. 
CHAP. XIV. 
PecuLiark SECRETIONS. 
U woer this head, it is our intention to consider the cir- 
cumstances under which light, electricity and caloric, are 
generated in the animal system. The subject is exceed- 
ingly interesting, and it has been enriched by numerous 
observations, the united efforts of the naturalist and che- 
mist. Still, however, there prevails a considerable diversi- 
ty of opinion, respecting the manner in which these sub- 
stances are produced, or the share which the vital princi- 
ple contributes towards their developement. As these bodies 
frequently appear to be produced contemporaneously, in the 
changes to which matter is subjected, they are to be view- 
ed in this chapter in connection, in expectation that the 
mode of production of one, may help to illustrate the ori- 
gin of antoher. 
I. LumrnousNEss or ANIMALS. 
Tue faculty of emitting light does not appear to be pos- 
sessed by any individuals of the classes Mammalia, Birds or 
Reptiles. Several fishes, however, exhibit this remarkable 
property ; particularly the Dorado, Mullet, Herring and 
Sprat. The Sparus chrysurus, an inhabitant of the seas 
ef Brazil, is said to be luminous in such a remark- 
