140 BIOLOGY AND ITS MAKERS 



But when the broad generalization, that all the tissues of 

 animals and plants are composed of cells, was given to the 

 world by Schleiden and Schwann, in 1838-39, the entire or- 

 ganization of living forms took on a new aspect. This was 

 progress in understanding the morphology of animals and 

 plants. 



Protoplasm. — With improved microscopes and attention 

 directed to cells, it was not long before the discovery was 

 made that the cells as units of structure contain protoplasm. 

 That this substance is similar in plants and animals and is 

 the seat of all vital activity was determined chiefly by the 

 researches of Max Schultze, published in 1861. Thus step 

 by step, from 1758, the date of the tenth edition of the 

 Systema Natures, to 1861, there was a progress on the mor- 

 phological side, passing from the organism as a whole to 

 organs, to tissues, to cells, and finally to protoplasm, the study 

 of which in all its phases is the chief pursuit of biologists. 



The physiological side had a parallel development. In 

 the period of Linmeus, the physiology of the organism was 

 investigated by Haller and his school; following him the 

 physiology of organs and tissues was advanced by J. Miiller, 

 Richat, and others. Later, Virchow investigated the physiol- 

 ogy of cells, and Claude Bernard the chemical activities of 

 protoplasm. 



This set forth in outline will be amplified in the follow- 

 ing chapters. 



