24 SCIENCE PROGRESS 



essential part and which simulate as a whole the properties 

 of enzymes. 



It has long been known that certain preparations can be 

 obtained from tissues of both plants and animals which have the 

 power of carrying active oxygen to certain oxidisable substances, 

 such as guaiaconic acid, salicylic aldehyde, tyrosin, etc., and 

 thereby causing the oxidation of these substances. These 

 various phenomena were very obscure until the researches 

 of Bach and Chodat threw light upon them. These observers 

 show that there are three distinct classes of bodies involved. 

 Firstly, organic peroxides of the type of substituted hydrogen 

 peroxide ; these are not enzymes, although they are decomposed 

 by boiling. Secondly, peroxydases, enzymes which act upon 

 the peroxides and produce active oxygen, which is capable of 

 oxidising certain bodies when these are present. The system, 

 peroxide and peroxydase, forms the oxidising agent, or oxydase 

 as it was originally called. In addition to these two classes 

 there is a third, also of enzyme nature, viz. the catalases, which 

 decompose hydrogen peroxide with evolution of inactive or 

 molecular oxygen and appear to act only on this particular 

 peroxide. These are widespread in both plants and animals, 

 but their function is not altogether clear, with the exception 

 of one important case to be mentioned immediately. The 

 "haemase" of blood investigated by Senter is one of these 

 catalases. Although the point of view taken by Bach and 

 Chodat undoubtedly tends to clear up much obscurity, it does 

 not explain all the facts known. The markedly specific nature 

 of certain "oxydases," such as tyrosinase and aldehydase, is 

 difficult to understand, and the mechanism by which the 

 peroxide takes up atmospheric oxygen after being decomposed 

 by the peroxydase, and thus reconstitutes itself, is as yet 

 unknown. 



Another complex system is that responsible for the activity 

 of the green leaf in the forming of starch and oxygen from carbon 

 dioxide and water. Important advances have recently been 

 made in this region by Ussher and Priestley. They show that 

 the system concerned consists of three partners the protoplasm 

 of the chlorophyll corpuscle, the chlorophyll itself, and a catalase. 

 By means of the pigment, acting as both chemical and optical 

 sensitiser, light energy is employed to cause reaction between 

 carbon dioxide and water in such a manner that formaldehyde 



