SARCOSPOBIDIA 35 



of the sheep than it does in those of the swine. It forms oval knots 

 several millimetres in diameter which, under certain conditions, may 

 attain the size of a hazel-nut. This stage in the development of the 

 parasite was formerly known as Balbiania gigantea. Cross-sections of 

 these knots show a very distinct alveolar network. Branching parti- 

 tions, formed of an anastomosing membrane, run from the surface to 

 the interior of the organism, enclosing numberless irregular polyhedral 

 chambers which do not communicate with one another. This alveolar 

 meshwork is also present in the Sarcosporide of swine, but, as the 

 chambers and spores are densely crowded, it can be seen only in very 

 thin sections or after breaking and emptying the individual chambers. 

 Each chamber represents a pansporoblast which has divided into 

 numerous spores. In the large Sarcosporides of sheep, spores are 

 found in those chambers only which lie near the surface of the 

 organism ; in the interior chambers they are broken up into a granular 

 mass. 



In order to examine single spores, one of the large Sarcosporides 

 from the gullet of the sheep should be teased out in natural lymph or 

 in normal saline. The naked spores are seen to be bean- to crescent- 

 shaped. Their plasm is finely granular and at one pole assumes 

 a differentiated structure, becoming, for about one-third its length, 

 somewhat paler in colour and obliquely striated. This modification 

 has been compared, though upon insufficient grounds, with the 

 nematocyst of the Myxosporides. Active movement in the spores 

 of the Sarcosporides of the swine and the sheep has not been proved. 

 It has, however, been observed in the Sarcosporide of the house-mouse, 

 where it takes the form of a forward progression, starting in jerks 

 by means of a screwing movement round the long axis of the organism. 

 For demonstration purposes, the parasites should be taken from 

 a freshly killed mouse and examined in a micro-incubator at blood 

 temperature. Osmotic changes and mechanical movements may 

 easily be mistaken for spontaneous movements. 



The spores should be stained in the following manner : A cover- 

 glass preparation of a single Sarcosporide is fixed in alcoholic solution 

 of mercuric chloride. It is coloured with haematoxylin or iron-hsematox- 

 ylin. The pole opposite to that at which the nucleus is situated 

 will appear paler and free from granulation, but a thread-cell or 

 nematocyst, such as is seen in the Myxosporides, is not present. The 

 single nucleus is comparatively large in size ; it is oval in shape, 

 being slightly elongated in the axis of the spore, and it is placed very 

 close to one polar extremity. 



Sarcosporides have been found in other mammals besides the 

 sheep and swine, as well as in several saurians (Platydactylus mauri- 

 tanicus, Lacerta muralis), and a large number of birds. In the few 



