Jan and Diane, let me try this again. 

All the babies studied were dead - the study compared the causes of death to thymus size. The babies who died of SIDS didn't die of anything ELSE, because other causes were ruled out. Kids who died of other stuff (poverty, infection, malnutrition) had smaller thymus glands than the ones who died of SIDS. Newer (since 1927) research has established that stress shrinks the thymus gland. The error in the 1889 research was in concluding that the non-SIDS dead babies were otherwise "normal," i.e. that smaller thymus glands were normal. The researcher concluded, erroneously, that the relatively larger thymus of the SIDS babies (who weren't otherwise sick, malnourished, etc) was abnormally large and that's what caused the SIDS. 

The problem lies in the definition of normal. If you define infants from poverty-stricken families who died of diahrrea, malnutrition, tuberculosis, etc as NORMAL, then well-nourished, healthy babies would therefore be defined as "abnormal." If then the "abnormal" babies died of something else, the conclusion was that their "abnormality" (the larger thymus glands) was associated with the cause of death. Follow that? Bad conclusion, because of a bad operational definition of "normal." 

BTW, the harmful practice of irradiating healthy babies' thymus glands "to help prevent SIDS" was described in pediatric texts until 1945; the practice continued into the 50's according to Dr. Nelson (of Nelson's Pediatrics) and described by Dr. Robert Sapolsky in chapter 8 of "Why Zebras Don't Get Ulcers." 

Linda Smith, Dayton OH where it's snowing tonight.