CONCLUDING REMARKS 155 



and animals is actually very recent, for, apart from a few pioneer 

 observations, our present not inconsiderable knowledge of the 

 subject is the result of work done during the last 25 years, and, 

 indeed, for the most part, during the last decade. Of late, more 

 and more workers have been attracted to the investigation of 

 the problems these elements present to the biologist, and with 

 the excellent research on these problems now being carried out 

 in various parts of the world, we may or may not find the list of 

 essential trace elements has to be increased, but we shall cer- 

 tainly see a rapid expansion in our knowledge of the physiology 

 and pathology of plants and animals in relation to the trace 

 elements. 



