Infection by _Coccidium oviforme_ is very common, without however presenting any symptoms by which the infection may be recognised. Usually the condition is only noted post-mortem, when the liver is found to be studded with numerous cascating tubercles, which on examination prove to be cystic areas crowded with coccidia. Sometimes too the liver of a rabbit dead from some intentional or accidental bacterial infection is found at the post-mortem to be marked by fine yellowish streaks and small tubercles due to the embryos of _Tænia serrata_, while the cystic form (_Cysticercus pisiformis_) is often noted free in the peritoneal cavity, or invading the mesentery. Abscess formation from infection with ordinary pyogenic bacteria occurs naturally in the rabbit, and frequently the animal house of a laboratory is decimated by an infective septicæmia due to _B. cuniculicida_. The ~Mouse~ and ~Rat~ suffer from septicæmia, and from the cysticercus form of _Tænia murina_; the cystic form (_Cysticercus fasciolaris_) of _T. crassicollis_ has its habitat in their livers. These small rodents are frequently infected with scabies, but if freely provided with clean straw will clean themselves by rubbing through it. The mouse is also attacked by favus, and the rat is often infected with _Trypanosoma Lewisi_. The ~Guinea pig~, like the rabbit, suffers from scabies and coccidiosis. In addition it is often naturally infected with _B. tuberculosis_, and it is a wise precaution to test animals as soon as they reach the laboratory by injecting Koch's Old Tuberculin--0.5 c.c. causing death in the tuberculous cavy within 48 hours. The ~Monkey~ is naturally prone to tuberculosis, and should be injected with 1 c.c. Old Tuberculin on arrival in the laboratory. The tissues of the monkey also serve as the habitat for a Nematode worm parasitic in cattle (_Oesophagostoma inflatum_) resembling the Anchylostomum, and this parasite frequently bores through the intestinal wall, and provokes the formation of small cysts in the immediately adjacent mesentery. The presence of these cysts may give rise to considerable speculation at the post-mortem. The ~Pigeon~ may be infected by _Hæmosporidia_, and its blood show the presence of halteridia. This bird may also be the subject of a bacterial infection known as pigeon diphtheria; while the fowl may be subject to scabies and ringworm, or suffer from fowl cholera or fowl septicæmia--infections due to members of the hæmorrhagic septicæmia group. ~Weighing.~--The larger animals are most conveniently weighed in a decimal scale provided with a metal cage for their reception instead of the ordinary pan (Fig. 166). Mice and rats are weighed in a modification of the letter balance, weighing to 250 grammes, which has a conical wire cage, (carefully counterpoised) substituted for its original pan (Fig. 167). [Illustration: FIG. 166.--Rabbit scales.]