314 HOW TO WORK 



resulting masses, as seen in fig. 357, but the formed material is per- 

 fectly passive- -as passive as a mass of mucus or fluid jelly would 

 be in which such self-moving, growing, dividing matter was placed. 



The production of formed material may also be studied in the 

 conversion of the white blood corpuscles into the red. In the frog 

 and newt, especially early in the spring, numerous white corpuscles 

 will be found the outer part of which is undergoing change, losing 

 its granular appearance, and becoming smooth and tinted. As the 

 corpuscle advances in age this process continues until at last the 

 oval red corpuscle is seen to contain only a small portion of 

 germinal matter in the interior, as represented in pi. XXXIII, 

 fig. 214. In mammalian animals generally this change goes much 

 further, and the whole corpuscle gradually undergoes conversion into 

 coloured formed material. The fully formed mammalian red cor- 

 puscle consists of matter in a colloid state, which very soon passes 

 into a crystalline form. In some instances, as in the case of the 

 blood corpuscle of the Guinea pig, this change occurs within a very 

 short time after the corpuscle has ceased to move, as when it is with- 

 drawn from the circulation of the animal and placed upon a glass 

 slide. In figs. 213, 216, pi. XXXIII, some of these crystals formed 

 from the red corpuscle of Guinea pig's blood are represented. 



Another simple case, showing the formation of formed material 

 from germinal matter, may be studied in cuticle, or in the cells upon 

 the papillae of the tongue. At first there is but a very thin layer of 

 formed material upon the surface of the germinal matter, and this is 

 soft, so that the mass may divide, and each portion may be invested 

 with a thin layer of this soft formed material. Nutrient pabulum 

 passes through it to the germinal matter within, and a portion of the 

 latter undergoes conversion into formed material. The germinal 

 matter increases, while at the same time new formed material is pro- 

 duced. This is shown in figs. 358, 359, 360, pi. LVII. In the 

 last figure, a thick layer of formed material has resulted, which only 

 permits a very little pabulum to pass through. The entire cell does 

 not, therefore, increase in size ; but the conversion of germinal 

 matter into formed material still proceeds, so that at last a mere 

 trace of the latter remains, and this often becomes liquefied and 

 removed. Thus a space or cavity (vacuole) remains and marks 

 where the living matter was situated. 



The bodies represented in figs. 355 to 360 are termed cells. 

 Cells of this simple character are very common, particularly in many 

 vegetable textures. It will be noticed, however, that they differ from 

 these last in the greater thickness of the formed material. Every one 

 of these cells consists of a portion of living germinal matter ; around 



