On the other hand, there is much clinical evidence to show that the European relapsing fever like various other types of the disease is transmitted from man to man by head and body lice (_Pediculus humanus_ and _Pediculus corporis_). Interesting supplementary evidence is that of Bayon's observations (1912), in Moscow. "Having visited the big municipal night hospitals at Moscow I soon noticed that they were kept with such scrupulous cleanliness, disinfected so lavishly, the beds of iron, the floor cemented, that it was not possible for bed-bugs to thrive to any extent on the premises. The people sleeping there were allowed, however, to sleep in their own clothes. The introduction of these model homes had not had any effect on the incidence of relapsing fever, for the places were still hot-beds of the fever during winter. On the other hand, though I changed my rooms several times, I found bugs in every successive lodging, and I was told in Moscow, this can hardly be avoided. Yet no foreigner, or Russian of the better class, ever catches relapsing fever. To this may be added the fact that when I asked for clothes-lice and promised to pay a kopec for two, the attendants from the night hostel brought me next morning a small ounce bottle crammed with _Pediculus capitis_ (= _P. humanus_), and _Pediculus vestimentorum_ (= _P. corporis_) collected off the sleepers. If relapsing fever were transmitted by bed-bugs, it would be much more disseminated than it is at present in Moscow." Direct experimental evidence of the agency of lice in transmitting relapsing fever is especially clear in the case of a type of the disease prevalent in parts of North Africa. We shall consider this evidence later. OTHER TYPES OF RELAPSING FEVER OF MAN--In addition to the three types of human relapsing fever already referred to, several others have been distinguished and have been attributed to distinct species of spirochætes. The various spirochætoses of man are: African, caused by _S. duttoni_; European, caused by _S. recurrentis_; North African, caused by _S. berbera_; East African, caused by _S. rossi_; East Indian, caused by _S. carteri_; North American, caused by _S. novyi_; South American, caused by _S. duttoni_ (?). Nuttall (1912) in his valuable résumé of the subject, has emphasized that "in view of the morphological similarity of the supposedly different species of spirochætes and their individual variations in virulence, we may well doubt if any of the 'species' are valid. As I pointed out four years ago, the various specific names given to the spirochætes causing relapsing fever in man may be used merely for convenience _to distinguish strains or races_ of different origin. They cannot be regarded as valid names, in the sense of scientific nomenclature, for virulence and immunity reactions are not adequate tests of specificity."