102 M. ARMAND RUFFER. 



carmine or indigo powder suspended in water is injected under 

 the ectoderm of Bipinnaria asterigera or Phyllirrhoe 

 bucephalum, the coloured powder is soon taken into the in- 

 terior of the mesodermic cells. In Bipinnaria the carmine is 

 absorbed by both large and small cells ; in Phylirrhoe, on the 

 other hand, the powder is ingested by the small cells, the 

 larger ones containing dissolved carmine only. The small 

 particles of carmine are actually in the interior of cells, but 

 the larger particles of the same matter become surrounded by 

 numerous small cells which form plasmodia resembling the 

 giant-cells found in the pathological structures of vertebrata. 

 Similar plasmodia formed by mesodermic cells are formed 

 when a few drops of human blood are introduced under the 

 cuticle of Bipinnaria asterigera; the nuclei of such plas- 

 modia lie at the periphery, whilst the centre of the Plas- 

 modium contains a mass of red blood-corpuscles in different 

 stages of degeneration. 



Migrating cells also form a barrier around foreign bodies, 

 such as glass, cellulose, &c., which are introduced under the 

 skin of these animals ; but, in many cases, no plasmodia are 

 seen, so that the formation of the latter structures does not 

 necessarily follow on the introduction of foreign bodies into 

 these animals. 



Blood-vessels, if present, do not necessarily play a part in 

 the process of inflammation, for no transudation takes place 

 from them, provided the foreign body be introduced without 

 wounding a blood-vessel. Cohnheira^s dictum, therefore — 

 '' Ohne Gefasse keine Entziindung" — is not altogether correct, 

 or, as Metschnikoff brilliantly says, " Inflammation is, genea- 

 logically speaking, of a much older date than the formation of 

 vessels, and exudation is a comparatively late phenomenon.^^ 



Mesodermic cells, however, do not eat everything they 

 come across, but have the power of exerting a choice. Thus 

 the mesodermic cells of Phyllirrhoe make no attempt to destroy 

 the fresh eggs of Spheerechinus granularis injected under 

 the skin of the animal. Nay, more ; the eggs retain their 

 vitality, so that they may be fecundated artificially whilst 



